1. Field of the Invention
The present invention relates to a robot-mounted two-package-mixing coating device for supplying a coating gun mounted on the distal end of a robot arm with a base compound and a hardener to coat a workpiece, and an internal pressure explosion-proof robot having a robot arm including electric devices housed in a pressurization chamber which is supplied with air under pressure.
2. Description of the Related Art
There has been used a two-package-mixing coating device for mixing a base compound and a hardener with each other and discharging the mixture to coat an object such as an automotive body or the like. One known two-package-mixing coating device mounted on a robot is disclosed in Japanese laid-open patent publication No. 11-244743, for example.
Such a conventional robot-mounted two-package-mixing coating device will be described below with reference to FIG. 6 of the accompanying drawings. As shown in FIG. 6, a coating robot 1 has a robot arm 2 supporting a bell-shaped coating gun 3 on its wrist. The robot arm 2 also supports thereon a base compound control valve assembly 4a and a hardener control valve assembly 4b which are juxtaposed in the longitudinal direction of the robot arm 2. The robot arm 2 houses therein a base compound metering pump 5a and a hardener metering pump 5b which are combined with respective motors 6a, 6b. Between the control valve assemblies 4a, 4b and the coating gun 3, there is disposed a mixer 7 for mixing a base compound and a hardener that are supplied with each other and supplying the mixture to the coating gun 3.
The base compound control valve assembly 4a has a plurality of coating ports associated with respective valves, and the hardener control valve assembly 4b has a plurality of coating ports associated with respective valves. The valve associated with one of the coating ports of the base compound control valve assembly 4a is actuated to open the coating port to supply a desired base compound to the base compound metering pump 5a, and the valve associated with one of the coating ports of the hardener control valve assembly 4b is actuated to open the coating port to supply a desired hardener to the hardener metering pump 5b. The base compound metering pump 5a and the hardener metering pump 5b are controlled for the ratio of their rotational speeds by the motors 6a, 6b to supply the base compound and the hardener at desired rates to the mixer 7. The mixer 7 mixes the base compound and the hardener with each other, and supplies the mixture to the coating gun 3, which atomizes and applies the mixture to a workpiece (not shown) to be coated.
With the conventional robot-mounted two-package-mixing coating device, the base compound control valve assembly 4a and the hardener control valve assembly 4b are juxtaposed and mounted on the robot arm 2. Therefore, an electropneumatic transducer (not shown) for turning on and off the supply of air to the valves of the base compound control valve assembly 4a and the hardener control valve assembly 4b is spaced from the base compound control valve assembly 4a and the hardener control valve assembly 4b by different distances.
Consequently, the valves of the base compound control valve assembly 4a and the hardener control valve assembly 4b respond to the supplied air at different times, failing to accurately regulate the mixing ratio of the base compound and the hardener. One solution would be to juxtapose the base compound control valve assembly 4a and the hardener control valve assembly 4b transversely across the robot arm 2. However, since the base compound control valve assembly 4a and the hardener control valve assembly 4b are relatively large in structure, the robot arm 2 would be required to have an increased transverse dimension that would be practically unacceptable.
The hardener is discharged at a rate smaller than the base compound, and a pipe for supplying the hardener is thinner than a pipe for supplying the base compound. The hardener is more viscous than the base compound. Therefore, it takes a considerable period of time to clean the interior of the pipe for supplying the hardener when coating colors are to be changed. Since the pipes extending from the base compound control valve assembly 4a and the hardener control valve assembly 4b to the coating gun 3 have substantially the same length, the pipe for supplying the hardener needs to be cleaned over an additional period of time even after the cleaning of the pipe for supplying the base compound has been completed. As a result, the tact time for changing coating colors is limited by the period of time required to clean the pipe for supplying the hardener.
The coating robot 1 is constructed as an internal pressure explosion-proof robot for use in a coating booth which contains an explosive atmosphere.
Japanese laid-open patent publication No. 10-138190, for example, discloses an internal pressure explosion-proof robot having a plurality of pressurization chambers which are hermetically sealed independently of each other without mutual communication and houses electric motors and cables. Air under pressure is supplied individually to the pressurization chambers through respective partitions.
With the above conventional internal pressure explosion-proof robot, the electric motors and the cables are accommodated in a robot arm which is basically of a tubular shape such as a cylindrical shape or a prismatic shape. The robot arm houses therein the partitions that define the pressurization chambers. If an explosion-proof structure is employed in a portion of the robot arm, then the internal structure of the robot arm becomes considerably complex, making the robot highly costly to manufacture.
It is a general object of the present invention to provide a robot-mounted two-package-mixing coating device which is of a simple structure capable of supplying a coating gun with a base compound and a hardener highly accurately at a desired mixing ratio, coating a workpiece with a high-quality coating layer stably, and cleaning supply pipes in a reduced period of time.
A major object of the present invention is to provide an internal pressure explosion-proof robot which is of a simple structure and has a desired explosion-proof structure that can easily be incorporated.
According to the present invention, a robot-mounted two-package-mixing discharging device has a robot arm with a coating gun mounted on a distal end thereof, and a base compound supply control mechanism, an electropneumatic transducer, and a hardener supply control mechanism which are mounted in the robot arm and successively arranged in the robot arm in the order named toward the coating gun. Since the electropneumatic transducer is disposed between the base compound supply control mechanism and the hardener supply control mechanism, passages for supplying air from the electropneumatic transducer to the base compound supply control mechanism and the hardener supply control mechanism have respective lengths that are substantially the same as each other. The base compound supply control mechanism and the hardener supply control mechanism can thus respond at the same time to air supplied from the electropneumatic transducer. The base compound and the hardener are thus discharged at stable rates and mixed highly accurately at a desired mixing ratio. As a result, a high-quality coating layer can be applied to a workpiece.
The hardener supply control valve mechanism is positioned more closely to the coating gun than the base compound control valve mechanism. Therefore, a hardener supply passage is shorter than a base compound supply passage, and the time required to clean the hardener supply passage is effectively reduced. As a consequence, the cleaning process that is carried out when coating colors are changed in the coating device is efficiently performed.
According to the present invention, an internal pressure explosion-proof robot has a robot arm constructed of a steel bar having an I-shaped or H-shaped cross section, and a lid mounted on at least one side of the robot arm, providing a closed pressurization chamber defined by the robot arm and the lid. Consequently, the robot arm itself maintains a desired level of mechanical strength with a simple and inexpensive structure, and allows a desired explosion-proof structure to be incorporated in a portion thereof. The explosion-proof structure is simple and highly versatile.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.